LTE systems provide reference signals (RSs) for measuring wireless channel characteristics. In LTE Release Version No. 8 (Rel-8), many wireless communications facilities employ cell-specific reference signals (CRSs). For example, physical downlink shared channel (PDSCH) demodulation, reference signal received power (RSRP) and reference signal received quality (RSRQ) (RSRP/RSRQ) measurements to rank candidate cells for handover and cell reselection decision, channel quality indicator (CQI) feedback, precoding matrix indicator (PMI) feedback, rank indication (RI) feedback, and other parameters all use CRSs.
In Rel-10, a transition was made from a fundamentally CRS-centric system to a system using UE-specific RSs. The UE-specific RSs now include demodulation reference signals (DMRSs) and cell-specific channel-state information (CSI) reference signals (CSI-RSs) the UE uses to acquire channel-state information. These UE-specific RSs fulfill a number of design goals including reducing the RS overhead, providing interference measurability, reducing RS interference for Coordinated Multi-Point (CoMP) transmission/reception (e.g. CoMP scenario 4 characterized by one common cell-ID shared among multiple cells), and other goals.